In general, organic molybdenum compounds are known to improve the lubricating properties of engine oils. For example, molybdenum dithiocarbamates are typically employed for the reduction of friction. The molybdenum dithiocarbamates, however, contain sulfur and slowly lose the ability to reduce friction unless an alternate sulfur source is present in the lubricating oil. Another example of organic molybdenum compounds are sulfurized molybdenum polyisobutenyl succinimide complexes which are used to mediate wear, reduce friction, and/or control oxidation. See, e.g., U.S. Pat. Nos. 4,259,194; 4,265,773; 4,283,295; 4,285,822; and 6,962,896 and U.S. Patent Application Publication No. 2005/0209111. Problems associated with the use of sulfur in lubricating oils are that sulfur can be incompatible with emission control devices and can result in corrosion problems.
U.S. Pat. Nos. 4,357,149 and 4,500,439 disclose molybdated C15-C20 alkenyl succinimides. In Example XI of both of these patents, a molybdated succinimide is prepared by reacting a C15-C20 alkenyl succinic anhydride with triethylene tetramine followed by treatment with a molybdic acid solution.
Russian Patent No. 2201433 discloses a molybdated succinimide post-treated with maleic anhydride as an additive for motor oils used in internal combustion engines. Russian Patent No. 2201433 further discloses that the additives are prepared by reacting an alkenyl succinimide of polyethylene polyamine with ammonium molybdate in the presence of water as a promoter and then reacting the resulting product with maleic anhydride taken in amounts of 0.2 to 1.0 mole per 1 mole of alkenyl succinimide of polyethylene polyamine. All of the examples disclosed in Russian Patent No. 2201433 employ a high molecular weight polyisobutenyl (950 M.W.) succinic anhydride (PIBSA) in preparing the alkenyl succinimide of polyethylene polyamine.
Molybdenum succinimide complexes are also described in U.S. Patent Application Publication No. 2009/0325833. These complexes when derived from high molecular weight alkylamines exhibit good friction, wear and oxidation inhibition. These complexes are prepared by post-treating the amine portion of the succinimide with maleic anhydride, at a charge mole ratio of maleic anhydride to succinimide of about 1:1, followed by a further post-treatment with molybdenum trioxide.